THE EVALUATION OF STAINLESS STEEL PITTING IN NEAT CORROSION INHIBITOR PRODUCTS - PART II

摘要

The resistance of the chromium oxide layer on stainless steel 316L (SS316L) to localized film breakdown and pitting when immersed in various neat chemical products at 55°C was previously evaluated using anodic cyclic polarization and electrochemical impedance spectroscopy (EIS). The focus of the previous research was to predict the compatibility of neat chemical products with SS316L, a commonly employed metallurgy for storage tanks and umbilical tubing. The investigation was aimed at assessing the influence of the immersion time and the applied anodic potential on pitting resistance. Based on the results, a small or non-existent passivation region and low polarization resistance values indicated that the SS316L material was susceptible to pit initiation and propagation in the neat chemical product in which it was immersed. The results demonstrated that EIS could be used as a quick tool to investigate the compatibility of neat chemical products with SS316L metallurgy. Nevertheless, some storage tanks are also made with a lower grade stainless steel 304 material (SS304). There is an interest for both chemical manufacturers and operators alike to determine if existing storage tanks made of SS304 are compatible and thus suitable for use with both current and potentially new products considering that the lower molybdenum content of SS304 lowers its pitting resistance in comparison with SS316L. This article presents the results from accelerated SS304 compatibility tests of neat chemical products using the same techniques: anodic cyclic polarization and EIS at 55°C. The objective is to corroborate that the criteria used to determine the compatibility for SS316L could be also implemented to evaluate the chemical compatibility with SS304.